Dual modulator displays are described in PCT Patent Application Publication Nos. WO02/069030, WO03/077013, WO2006/010244 and WO2008/092276 (collectively, the “Dual Modulator Display Applications”) which are hereby incorporated herein by reference. In some embodiments, such displays comprise a light source modulation layer and a display modulation layer. The light source modulation layer may be driven to produce a relatively low resolution representation of an image which is subsequently provided to the relatively high resolution display modulation layer. The low resolution representation generated by the light source modulation layer may be further modulated by the higher resolution display modulation layer to provide an output image which is ultimately viewed by the observer.
In some embodiments, the light source modulation layer may comprise an array of modulated light sources, such as light emitting diodes (LEDs), for example. Because the light source modulation layer typically illuminates the display modulation layer, the light source modulation layer may be referred to as a backlight or backlight modulation layer. In general, however, it is not required that the light source modulation layer be located behind the display modulation layer. The display modulation layer, which may be positioned and/or aligned to receive light from the light source modulation layer, may comprise a liquid crystal display (LCD) panel, for example.
Modulation at the light source modulation layer causes a spatially varying light pattern to be received at the display modulation layer. The brightness of the pixels on the display modulation layer is therefore affected by the variable localized brightness of the light received at the display modulation layer from the light source modulation layer. Determining the driving values for the display modulation layer may comprise using the driving values for the light source modulation layer to estimate the expected luminance pattern at the display modulation layer and then using this expected luminance to derive driving values for the display modulation layer.
The light emitted by the light source modulation layer may be relatively broad bandwidth light relative to the visible spectrum. Where broad bandwidth light is used to illuminate the display modulation layer, the resulting gamut of the display may be restricted since the wide bandwith light may be unable to produce highly saturated colors. In other displays, the light source modulation layer may comprise a plurality of relatively narrow band light sources (e.g. red, green and blue (RGB) LEDs). While using narrowband light sources in the light source modulation layer may increase the gamut of the display by providing the ability to output more highly saturated colors, the narrow bandwidth sources can cause metameric issues, where a color generated by the display may produce a color match (e.g. to a sample color) for one observer, but the same display color will not produce a color match for a different observer.
There are general desires to maximize or improve the color gamut of displays and to minimize or reduce metameric issues.
Dual modulator displays may also suffer from parallax issues when viewers are located off of the optical axis of the display. Such parallax issues may result, for example, because the degree to which different elements of the light source modulation layer illuminate corresponding elements of the display modulation layer vary with viewing angle. Accordingly, when a viewer is located off of the optical axis of the display, the viewer may see visible artefacts attributable to parallax.
There is a general desire to minimize or reduce parallax issues in dual modulator displays.